It consists of the melting on the raw compound making use of oxyhydrogen flame as well as crystallisation from the melted droplets to variety a cylinder. Graded 9 about the Mohs-hardness scale (graded 1-10), the resulting sapphire crystals are pretty much scratch-proof and very tough, making sure an unhindered eyesight https://www.watchesworld.com/top-10-dive-watches/